Function of Transistor

By: Ashok Negi

Function of transistor:-
Transistor is the building block of any computers it invented in Bell Lab in 1947. the transistor is a small electronic device used in all things digital from your digital watch to supercomputers. We therefore think some under standing of how transistors operate is required. To begin one need to know a little about the semiconductors. These fall under a class of materials that behave as either conductors or insulators depending on the certain conditions. Silicon, Germanium, and Gallium Arsenide are the most commonly used semiconductor can be of two types. An N-type which has a “excess” electrons-and p-type material, which has deficiency of electrons. The N or P is determined by an “impurity” element that is add to a pure semiconductor, the resultant material is N-type and if it has less electrons, you get a P-type material.
The simplest of semiconductor device is diode, which is formed when a P-type and an N-type material are brought together, adjacent to each other. The electron from the N-type fill up the deficiencies (called “holes”) in the P-type, which leaves a neutral layer at the junction that does not conduct. This “barrier” is over come by applying a small positive voltage to the diode. When the voltage is removed, the barrier is recreated, making the device not capable of conducting similarly, when a negative voltage is applied, the device does not conduct.
The transistor is a very simplistic way, can be thought of as two diodes joined back to back. We can therefore have two kinds of transistors P-N and P-N-P. Both these configurations can be used in devices; NPN is usually chosen for explanation. The three blocks that make up a transistor are the Emitter, the Base, and the Collector. The Emitter and collector are made from the same type of semiconductor, but you can’t interchange there connections-their width and the way they are manufactured are different.

When the blocks come together. Two barriers are formed-between the Emitter and base, and between the base and collector. Typical transistor operation sees that Emitter-base junction “forward-biased”- this mean the positive of the battery is connected to the base, which is P-type, and the negative battery terminal is connected to the Emitter, which is N-type. This ensures that the barrier between these two terminal is eliminated. Similarly, the base collector junction is “reverse-biased”. Now electrons are pushed from the emitter into the base. The collector has a positive voltage applied to it which there fore draws (the negatively charged) electrons that comes to the base from the Emitter are drawn into the collector. Which leads to a corrent flow in the device? The device is now in the on state. When the voltage is applied to the emitter-base junction is removed or its polarity reversed. The barrier at the Emitter base junctions’ reappears and the current flow stops. The transistor is now in the off state.

The switch action is most important capability of a transistor which is used in a digital circuits such as those in computers. Computer work by treating all data as a series of the 1s and os, or on and off states. Transistor are performed complex calculations based on long series of 0s and 1s:a 32 bit CPU can add, subtract and perform several functions on data that contains a total of 32 0s and 1s. for each 0 and 1 that needs to be stored or operated upon in a CPU, one transistor is needed .in order to store two 64-bit numbers, a total of 128 transistors is required this is only to store the number during calculation: for each operation such as multiplication or comparison, a thousand or more transistors are required. Today’s CPUs have millions of transistors to perform the myriad calculations that make games, video editing. And so on work for us. All these millions of transistors are basically working in a switching mode- in an on or an off state at any given time.